1. Field of the Invention
The invention is generally related to a method for forming crosslinked chitosan support materials, including crosslinked and functionalized chitosan support materials, and crosslinked chitosan products obtained by this method.
2. Description of the Related Art
Hydrogel beads are products frequently prepared from polysaccharides, especially agarose, dextran and cellulose. Hydrogel beads from chitosan are also generally known.
Chitosan is the acid-soluble deacetylation product of chitin. For example, chitosan is the product of alkaline hydrolysis of abundant chitin produced in the crab shelling industry. Chitosan, a biopolymer soluble in dilute (0.1 to 10%) solutions of carboxylic acids, such as acetic acid, is readily regenerated from solution by neutralization with alkali. In this manner, chitosan has been regenerated and reshaped in the form of films, fibers, and hydrogel beads. For instance, chitosan beads are prepared in one conventional method by precipitating dilute solution of chitosan in acetic acid into alcoholic or aqueous sodium hydroxide followed by solvent exchange with water.
However, in contrast to beads from cellulose, which are insoluble in most organic solvents, acids and bases, chitosan retains the solubility in dilute acids of the parent biopolymer. This solubility is typically overcome by inducing crosslinking. A conventional chitosan crosslinking reaction involves dialdehydes, such as glutaraldehyde, or diglycidyl ethers, such as butanediol diglycidyl ether, or epoxides like epichlorohydrin. Chitosan beads crosslinked with diglycidyl ethers are commercially available under the trade name CHITOPEARL, as manufactured by Fuji Spinning, Ltd., Japan.
Also, various researchers have discussed blending chitosan and cellulose to produce biodegradable films (see, for example, U.S. Pat. No. 5,306,550 to Nishiyama et al.; Hosokawa et al., Ind. Eng. Chem. Res., 29:800-805 (1990); Hasegawa et al., J. Appl. Polym. Sci., 45:1873-1879 (1992)). Though cellulose contains only trace amounts of carbonyl groups, these trace amounts of carbonyl groups are suspected in the art to play an important role in crosslinking to chitosan to form a crosslinked polymeric network of cellulose and chitosan.
Also, it has been demonstrated that complexes of chitosan with acetic acid (viz., chitosonium acetate) are converted to chitin (i.e., the N-acetylamide of chitosan) by a heat-catalyzed amidification or dehydration reaction, in U.S. application Ser. No. 08/435,866 to Glasser et al., filed May 5, 1995. The amidification reaction described in U.S. application Ser. No. 08/435,866 converts acid-soluble chitosan into acid-insoluble chitin.
Because chitosan is easily solubilized and processed, a great deal of research in the hydrogel field has been devoted to experimentation with and/or use of chitosan in a wide variety of applications. Therefore, the art would be highly interested in a new technique to form crosslinked chitosan support material, such as crosslinked chitosan beads, in a simplified, reliable manner.